On-chip inductor with magnetic core

ABSTRACT

An inductor formed on an integrated circuit chip including one or more inner layers ( 12 ) between two or more outer layers ( 14 ), inductor metal winding turns ( 16 ) included in one or more inner layers ( 12 ), and a magnetic material forming the two or more outer layers ( 14 ) and the one or more inner layers ( 12 ). In one embodiment, the magnetic material is a photoresist paste having magnetic particles. In another embodiment, the magnetic material is a series of magnetic metallic strips ( 32  and  36 ) disposed on each of the first and second portions ( 30  and  34 , respectively) of the two or more outer layers ( 14 ) and on each of the one or more inner layers ( 12 ). The series of magnetic metallic strips on the first and second portions ( 30, 34 ) form a grid pattern. Other embodiments include an adjustable controlled compound deposit and control windings with adjustable electrical currents.

BACKGROUND OF INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an inductor on an integratedcircuit chip, and in particular to an inductor having a magnetic core onan integrated circuit chip.

[0003] 2. Background of the Invention

[0004] In recent integrated circuit chip design, it is often desired toprovide passive electrical devices such as inductors directly on thechip as part of the integrated circuit. Inductors are required invarious microelectronic applications, e.g. voltage control oscillatorsand power amplifiers.

[0005] In addition, inductors are often used in radio frequency (RF)circuits such as those used in devices like cellular telephones,wireless modems, and other types of wireless communication equipment. Aninductor joined in series or parallel with a capacitor can form afrequency resonator or filter unwanted signals.

[0006] However, due to the limited space on an integrated circuit chipand highly competitive chip market, on-chip inductors must fit within alimited space and be inexpensive to fabricate. In that regard, it isdesirable for an on-chip inductor to have a high inductance per unitarea.

[0007] Prior art on-chip inductors with air core have encountered manyproblems.

[0008] Typically, they require too much space on the integrated circuitchip. Often, the Q factor of the air core on-chip inductor is too low.Many prior art on-chip inductors include an air core inductor that hasan open magnetic field. Such designs often generate interference and/orunwanted magnetic coupling that may cause instability problems. Inaddition, prior art air core on-chip inductors often exhibit an eddycurrent in the near metal or substrate of low volume resistivity thatfurther reduces the inductor's Q value. Another shortcoming of prior artair core on-chip inductors is that their inductances are not adjustable.A lack of adjustability results in a low yield rate when processvariations occur. Finally, prior art air core on-chip inductors are notsuitable for very high frequency applications, i.e., higher than 10 GHz,because their large size presents large parasitic capacitance and theself-resonate frequency would be lower than the operation frequency.

SUMMARY OF INVENTION

[0009] One aspect of the present invention is an inductor formed on anintegrated circuit chip. The inductor includes two or more outer layers,one or more inner layers between the two or more outer layers, inductormetal winding turns included in the one or more inner layers, and aphotoresist paste having magnetic particles. The photoresist paste atleast partially forms the two or more outer layers and the one or moreinner layers.

[0010] Another aspect of the present invention is an inductor formed onan ntegrated circuit chip, the inductor including two or more outerlayers each including a first portion and a second portion, one or moreinner layers between the two or more outer layers, inductor metalwinding turns included in the one or more inner layers, and a series ofmagnetic metallic strips disposed on each of the first and secondportions of the two or more outer layers and on each of the one or moreinner layers. The series of magnetic metallic strips on the firstportion and the second portion are arranged so as to form a gridpattern.

[0011] Still another aspect of the present invention is a method offorming an inductor having a magnetic core. The method includes thefollowing steps: providing one or more chambers, each having one or moremetals disposed therein; heating the one or more metals so as togenerate vapors of the one or more metals; forming a magnetic materialfrom the vapors of the one or more metals; providing an integratedcircuit chip having at least one silicon oxide layer, the at least onesilicon oxide layer having an etched opening; and depositing themagnetic material in the etched opening of the at least one siliconoxide layer.

[0012] Yet another aspect of the present invention is an inductor formedon an integrated circuit chip, the inductor including two or more outerlayers, one or more inner layers between the two or more outer layers,inductor metal winding turns and a control winding in the one or moreinner layers, and at least one of a soft magnetic core material and ahard magnetic core material included in each of the two or more outerlayers and the one or more inner layers.

[0013] Other features, utilities and advantages of various embodimentsof the invention will be apparent from the following more particulardescription of embodiments of the invention as illustrated in theaccompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

[0014] For the purpose of illustrating the invention, the drawings showa form of the invention that is presently preferred. However, it shouldbe understood that the present invention is not limited to the precisearrangements and instrumentalities shown in the drawings, wherein:

[0015]FIG. 1 is a cross-sectional view of a magnetic core inductoraccording to one embodiment of the present invention;

[0016]FIG. 2A is a plan view of a top layer of one magnetic coreinductor according to one embodiment of the present invention;

[0017]FIG. 2B is a plan view of a middle layer of one magnetic coreinductor according to one embodiment of the present invention;

[0018]FIG. 3A is a top plan view of a top layer of one magnetic coreinductor according to one embodiment of the present invention;

[0019]FIG. 3B is a top plan view of an intermediate layer of onemagnetic core inductor according to one embodiment of the presentinvention;

[0020]FIG. 3C is a top plan view of a middle layer of one magnetic coreinductor according to one embodiment of the present invention;

[0021]FIG. 4 is a schematic illustration of an apparatus for fabricatingthe magnetic core layers of the present invention and a cross-sectionalview of material used to make the magnetic core layers;

[0022]FIG. 5 is a cross-sectional view of a ferrite magnetic coreinductor with bias magnetic field of hard magnetic material according toone embodiment of the present invention;

[0023]FIG. 6 is a cross-sectional view of a magnetic core inductorhaving a control winding disposed around a core including both soft andhard magnetic materials according to one embodiment of the presentinvention; and

[0024]FIG. 7 is a cross-sectional view of a magnetic core inductorhaving a control winding disposed around a core including soft magneticmaterial according to one embodiment of the present invention.

DETAILED DESCRIPTION

[0025] The present invention is an on-chip inductor having a magneticcore. The magnetic core allows the inductor to have a reduced size andan increased Q value. The magnetic field of the inductor is contained tothe magnetic core to form a closed magnetic loop thereby improvingcircuit stability. In one embodiment, the level of inductance may becontrolled. In another embodiment, the use of ferrite allows forhigh-speed applications. The various conductive, insulating, andmagnetic layers and cores described herein may be formed by any suitablemethod known to those skilled in the art, including but not limited tosputtering, electroplating, chemical vapor deposition, plasma enhancedchemical vapor deposition, physical vapor deposition, and the like.

[0026]FIG. 1 illustrates a cross-sectional view of a representativebasic structure of an on-chip inductor 10 according to one embodiment ofthe present invention. An inner layer 12 is located between outer layers14. Inductor metal winding turns 16 are located within inner layer 12and disposed around a magnetic material, referred to as magnetic core 18herein. Magnetic core 18 is also located on the outsides of inductormetal winding turns 16. In addition, outer layers 14 are made up ofmagnetic core 18. Gaps 20 between each of outer layers 14 and innerlayer 12 may help avoid magnetic flux saturation. In addition, becausethe width of each of gaps 20 is very small, the magnetic field leakageof the gaps is negligible. In other embodiments, the width of each ofgaps 20 may be reduced to zero to form a completely closed magnetic loopthereby maximizing inductance and the Q value of the inductor. As oneskilled in the art will appreciate, other embodiments may include any ofmyriad configurations that include greater than one of any or both ofinner layer 12 or outer layers 14.

[0027] Utilizing the structure described above with respect to FIG. 1,alternative embodiments of the present invention may be developed havingvarying magnetic core materials and providing different performancecharacteristics. FIGS. 2A and 2B illustrate the particular magnetic corematerials that are included in the layers of a three-layer embodiment.As illustrated in FIG. 2A, at least surface 22 of outer layers 14 aresubstantially made of a photoresist paste containing a powder ofmagnetic material (as discussed in greater detail below). FIG. 2Billustrates inner layer 12 that includes an outside and center material26 surrounding an inductor metal wire turns 28. Outside material andcenter material 26 are also made of photoresist paste containing apowder of magnetic material. In addition, as one skilled in the art willappreciate, silicon oxide is typically positioned between outside andcenter material 26 and inductor metal wire turns 28, although othermaterials may also be used.

[0028] Photoresist paste electrically isolates discrete magneticparticles within the magnetic powder included in the paste. Theelectrical isolation causes a high resistance to develop between themagnetic particles in the photoresist paste. As a result, the eddycurrent is significantly reduced or eliminated, thus keeping the Q valueof the inductor high. The structure illustrated in FIGS. 2A and 2B maybe used with both metal-based magnetic materials and iron oxide-basedmagnetic materials.

[0029] There are typically two categories of basic magnetic materialsused in the present invention. The first category includes metal-basedmaterial such as Fe (iron), Ni (nickel), Cu (copper), Mo (molybdenum),Mn (manganese), Cr (chromium), etc. The second category includes ironoxide based material, i.e., ferrite, such as MnFe₂O₃, CuFe₂O₃, ZnFe₂O₃,NiFe₂O₃, etc. The magnetic photoresist paste is typically produced bymixing either metal or ferrite powder, i.e., magnetic powder, withintegrated circuit chip compatible pastes such as SILK or polyimide. Themagnetic powder may have particle sizes as small as the nanometer range.

[0030] Although the structure illustrated in FIG. 1 has three layers, inorder to increase the magnetic loop cross-sectional area and increasethe turns of the inductor, structures of more than three layers may beused. For example, a six-layer structure may be fabricated where layers1, 2, 5, and 6 are as illustrated in FIG. 2A and layers 3 and 4 are asillustrated in FIG. 2B.

[0031]FIGS. 3A-3C illustrate an alternative embodiment of on-chipinductor 10. This embodiment of inductor 10 has a three-layer structurehaving strips of metal-based magnetic materials. The layers are arrangedto develop a particular pattern. Layers 1 and 3 each include a firstportion 30 having horizontally arranged magnetic strips 32 asillustrated in FIG. 3A and a second portion 34 having verticallyarranged magnetic strips 36 as illustrated in FIG. 3B. In oneembodiment, the particular pattern developed by magnetic strips 32 andmagnetic strips 36 is a perfect orthogonal grid pattern. Othertransverse patterns are also encompassed by the present invention. Layer2 includes inductor metal wire turns 38 surrounded by horizontallyarranged strips of magnetic material 39.

[0032] Vapor deposition or sputtering may be used to deposit themetal-based magnetic materials used in the embodiment of inductor 10shown in FIGS. 3A-3C. Vapor deposition produces a high density ofmagnetic materials, but undesirably high eddy currents may result whenthe magnetic materials are deposited with certain configurations. Toaddress this problem, strips 32, 36, and 39 are deposited in aparticular pattern in the various layers of inductor 10 described above.This pattern significantly reduces or eliminates the eddy currentsthereby keeping the Q value of the inductor high. As one skilled in theart will appreciate, alternative layering patterns may also be used solong as they provide the same advantages as the embodiment illustratedin FIGS. 3A-3C.

[0033] Referring now to FIG. 4, the present invention includes a methodof generating iron oxide-based magnetic material and depositing it oninductor cores. The method allows for an adjustable, controllablecompound deposit of magnetic materials on inductor cores. As part of themethod, process equipment, including box-like first chamber 40 andsecond chamber 42, located in an oxygen environment 44, is provided.First chamber 40 is defined by a chamber wall 46 within which is locatedan electric heater 48 and a metal element 50. A portion of chamber wall46 includes an adjustable aperture 52. Second chamber 42 is defined by achamber wall 53 that includes an electric heater 54 and a metal element56. A portion of chamber wall 53 includes an adjustable aperture 60. Aspart of the method of generating iron oxide-based magnetic material,iron oxide-based magnetic material is deposited in an etched opening 62in a silicon oxide layer 64 that forms the inductor core.

[0034] Both first chamber 40 and second chamber 42 generate a vapor ofmetal (not shown). The vapor flow of first chamber 40 and second chamber42 is controlled by adjusting apertures 52 and 60, respectively, and thecurrent flowing to heaters 48 and 54, respectively. In one embodiment,metal 50 and metal 56 are two-component metals in an iron oxide-basedmagnetic material, e.g., iron and nickel. In oxygen environment 44, thevapor of iron and vapor of nickel form iron oxide-based magneticmaterial compound, i.e., NiFe₂O₃. The compound is deposited in etchedopening 62 on silicon oxide layer 64. As one skilled in the art willunderstand, the proper flows of iron and nickel are achieved bycontrolling the oxygen density and temperature.

[0035]FIGS. 5, 6, and 7 illustrate additional embodiments of theinductor 10 of the present invention. FIG. 5 illustrates across-sectional view of a representative base structure of an on-chipinductor structure 70 for use in very high frequency applications, i.e.,greater than 10 GHz. On-chip inductor structure 70 includes an innerlayer 72 between outer layers 74. Inductor metal wire turns 76 arelocated within inner layer 72 and are disposed around a soft magneticmaterial referred to herein as soft magnetic core 78. Unlike on-chipinductor structure 1 0 in FIG. 1, in on-chip inductor structure 70, ahard magnetic material referred to as hard magnetic core 79 herein isadjacent one side of inductor metal wire turns 76. Outer layers 74 aretypically made up of soft magnetic core 78. Both the soft and hardmagnetic materials utilized in structure 70 are typically ferrite-based,although other materials may be used in certain applications. As in FIG.1, various gap widths may exist between inner layer 72 and each of outerlayers 74. In addition, the alternative embodiments, more than one ofany, all, or any combination of inner layer 72 and outer layers 74 maybe present.

[0036] Residual magnetic flux density and coercive force are twomagnetism performance parameters used to categorize two typical kinds ofmagnetic materials used in the present invention. The first kind ofmagnetic material is a soft magnetic material that has a low residualmagnetic flux density and a small coercive force. The soft magneticmaterial is used to increase the inductances and improve Q values ofinductors in the invention. The second kind of magnetic material is ahard magnetic material that has a high residual magnetic flux densityand a large coercive force. The hard magnetic material is used to set abias magnetic field for the operation point in the invention.

[0037] As one skilled in the art understands, an iron oxide-basedmagnetic material such as ferrite is typically used for very highfrequency applications. However, its initial permeability is very smallat an external magnetic field H of zero. Thus, an external magneticfield is required to set an operation point where the permeability islarge. In practice, when on-chip inductor structure 70 that includesboth soft and hard magnetic materials is heated to a temperature inexcess of the Curie temperature, i.e., 300° to 6000° C., the hardmagnetization material used in hard magnetic core 76 loses itsmagnetization or exhibits spontaneous magnetization. Thus, whenintegrated circuit chips containing on-chip inductor structure 70 arepackaged, they require an external magnetic field to activate the hardmagnetic material in hard magnetic core 79. The re-magnetized hardmagnetic core 79 sets a bias magnetic field for the ferrite. The biasmagnetic field increases the permeability to the required operationpoint for ferrite. Ferrite may have very high volume resistivity andvery low loss so that it may operate at very high frequency, i.e., up tomore than 100 GHz. Since the relative permeability of ferrite is nearone at zero magnetic field, i.e., the initial permeability is close to1, it needs a bias magnetic field to set the operation point with largerelative permeability. It also provides the conditions required toadjust the relative permeability of ferrite by change of the biasmagnetic field. In addition, as with the embodiment illustrated in FIG.1, the embodiment illustrated in FIG. 5 may include other configurationsproviding a combination of soft and hard magnetic materials are used.

[0038]FIGS. 6 and 7 illustrate cross-sectional views of a representativebase structure of an on-chip inductor structure 80 that allows foradjustability of the inductor's inductance. On-chip inductor structure80 includes an inner layer 82 in between outer layers 84. Inductor metalwire turns 86 are located within inner layer 82 and disposed around asoft magnetic material referred to as soft magnetic core 88 herein.Unlike the structure illustrated in FIGS. 1 and 5, adjacent one side ofinductor metal wire turns 86 is a control winding 90. In the embodimentillustrated in FIG. 6, control winding 90 is disposed around a core 92having both a soft magnetic material referred to as soft magnetic core94 and a hard magnetic material referred to as hard magnetic core 96.Outer layers 84 are typically made up of soft magnetic core 88. Ofcourse, as illustrated in FIG. 7, in other embodiments, core 92 may onlyinclude soft magnetic material 94. Both the soft and hard magneticmaterials utilized in the structure illustrated in FIGS. 6 and 7 aretypically ferrite-based, although other materials may be used in certainapplications. As in the above-described embodiments, the structuresillustrated in FIGS. 6 and 7 may include various gap widths betweeninner layer 82 and outer layers 84. In addition more than one of each ofinner layer 82 and outer layers 84 may be present.

[0039] In practice, a DC current applied to control winding 90 generatesthe bias magnetic field necessary to reach the operation point of theferrite magnetic materials used in both soft magnetic cores 88 and core92. The permeability may be adjusted by tuning the current so that theinductance is adjustable as well.

[0040] The on-chip inductor of the present invention offers a variety ofbenefits. By using magnetic material in the core of the inductor, thesize of the inductor is reduced and the Q value is increased. In thepresent invention, the magnetic field of the inductor is closed in themagnetic core thereby reducing interference with other chip components.Use of ferrite in the inductor core allows the inductor to operate atvery high frequencies. Finally, by changing the DC magnetic bias using acontrol winding, the inductance of the inductor may be controlled oradjusted.

[0041] While the present invention has been described in connection withspecified embodiments, it will be understood that it is not so limited.On the contrary, it is intended to cover all alternatives, modificationsand equivalents as may be included within the spirit and scope of theinvention as defined in the appended claims.

1. An inductor formed on an integrated circuit chip, the inductorcomprising: two or more outer layers; one or more inner layers betweensaid two or more outer layers; inductor metal winding turns included insaid one or more inner layers; and a photoresist paste having magneticparticles, said photoresist paste at least partially forming said two ormore outer layers and said one or more inner layers.
 2. An inductoraccording to claim 1, wherein said photoresist paste substantiallysurrounds said inductor metal winding turns.
 3. An inductor according toclaim 1, wherein said magnetic particles are substantially metal-based.4. An inductor according to claim 1, wherein said magnetic particles aresubstantially iron oxide-based.
 5. An inductor according to claim 1,further comprising gaps between each of said two or more outer layersand said one or more inner layers.
 6. An inductor formed on anintegrated circuit chip, the inductor comprising: two or more outerlayers each including a first portion and a second portion; one or moreinner layers between said two or more outer layers; inductor metalwinding turns included in said one or more inner layers; and a series ofmagnetic metallic strips disposed on each of said first and secondportions of said two or more outer layers and on each of said one ormore inner layers, said series of magnetic metallic strips on said firstportion and said second portion arranged so as to form a particularpattern.
 7. An inductor according to claim 6, wherein said particularpattern is a perfect orthogonal grid pattern.
 8. An inductor accordingto claim 6, wherein said particular pattern is a transverse gridpattern.
 9. An inductor according to claim 6, wherein said series ofmagnetic metallic strips substantially surrounds said inductor metalwinding turns.
 10. An inductor according to claim 6, further comprisinggaps between each of said two or more outer layers and said one or moreinner layers.
 11. A method of forming an inductor having a magnetic corecomprising the steps of: providing one or more chambers, each having oneor more metals disposed therein; heating said one or more metals so asto generate vapors of said one or more metals; forming a magneticmaterial from said vapors of said one or more metals; providing anintegrated circuit chip having at least one silicon oxide layer, said atleast one silicon oxide layer having an etched opening; and depositingsaid magnetic material in said etched opening of said at least onesilicon oxide layer.
 12. A method according to claim 11, wherein atleast one of said one or more metals is iron and at least one of saidone or more metals is nickel.
 13. A method according to claim 11,wherein said magnetic material is iron oxide-based.
 14. A methodaccording to claim 11, wherein each of said chambers has a chamber wallwith an adjustable aperture and said chambers are located in an oxygenenvironment, said oxygen environment having an oxygen density and atemperature.
 15. A method according to claim 14, wherein said formingstep is controlled by controlling said oxygen density, said temperature,and said adjustable apertures.
 16. An inductor formed on an integratedcircuit chip, the inductor comprising: two or more outer layers; one ormore inner layers between said two or more outer layers; inductor metalwinding turns and a control winding in said one or more inner layers;and at least one of a soft magnetic core material and a hard magneticcore material included in each of said two or more outer layers and saidone or more inner layers.
 17. An inductor according to claim 16, whereinsaid control winding is disposed around a core including said softmagnetic material and said hard magnetic material.
 18. An inductoraccording to claim 16, wherein said soft magnetic core material and saidhard magnetic core material are substantially iron oxide-based.
 19. Aninductor according to claim 16, wherein said control winding is disposedaround a core including only said soft magnetic material.
 20. Aninductor according to claim 16, wherein said hard magnetic core materialis adapted to create magnetic biasing within the inductor.
 21. Aninductor according to claim 16, wherein said inductor metal windingturns is disposed around a core including said soft magnetic material.22. An inductor according to claim 16, wherein said control winding isadapted to receive an electrical current.